Siftproof bag bottom



June 17, 1952 M. E. CRAIG 2,600,487

SIFTPROOF BAG BOTTOM Filed July 6. 1948 2 Sl-lEETS-SHEET 1 INVENTOR. MERLE E CRAIG ATTOR N E! June 17, 1952 M. E. CRAIG SIFTPROOF BAG BOTTOM 2SHEETS-SHEET 2 Filed July 6, 1948 INVENTOR. MERLE E CRAIG.

ATTORNEY Patented June 17, 1952 .SIETPROOF BAG BOTTOM Merle Craig,Camas, Wash 'assignor to Crown -Zellerbach Corporation, San Francisco,Calif.,

a'corporation-of Nevada 7 Application July 6, 1948, Serial No. 37,232'

'1 Claim. 1 This invention relatesto-multi-ply paper bags having pastedbottom ends.

'More particularly this invention relates to with a bottom which willremain sift-proof.

From' time to-timevarious improvements have been made in pasted bagbottoms in an endeavor to make them more nearly sift-proof, among whichthe improvements described'in'U'S. Letters Patent No. 1,960,929, issuedMay 29, 1934, to

Taggert, are particularly well known. While the adoption of some ofthese improvements by the trade has resulted in'some reduction in lossin the shipping of carbon black, nevertheless, I have found, in thecourse of considerable observation and experience in the handling ofbags of carbon black,that the percentage ofthese bags which are foundto'be ruptured or leaky is still fairly large in spite of suchimprovements.

In mystudy of this-problem Ihave'found that these bag failures arelargely attributable to the following causes:

(1) Failure in a pasted seam of one of the bot tom'flaps;

(2) Tearing'occurring in a ply where an end slit had been made informing the bag bottom;

(3) Formation of'bag bottom in such'manner that unequal or excessivestrain is imposed on one of the plies'alone.

Observance of failures occurring in the pasted seams in the bottoms ofcarbon black bagsand tests which I'have made in this connection, haveshown that such'failures inthe pasted seams are less apt'to'occur if theapplication of the paste has takenplace'on'both of the opposed surfacesor faces which are pasted one over the other, than when the paste isapplied to'only one of the'faces. In other words, when'a flap is foldedover and pasted down on the bag bottom, I have found that there is lesslikelihood-of any failureoccurring along the pasted seamlines-if thepaste has been applied not only on the underside of the fiapbut also onthe'surface to which such underside of the flap is to be secured. Thiswill be readily understood as'one considers the-speed and the'manner inwhich paste is applied for the seams in modern bag machines.

One of the objects of the present invention therefore is to provide animproved bag bottom structure'in'which such double application ofpastewill' occur along a greater extent of the bottom seam withoutnecessitating any change in the present manner or method of applyingpaste.

While tearing of the paper at the ends of the slits, which slitsare'required' to be made in the plies to form the bottom sections ofstandard types of bags, may be due to one cause or another, obviouslyreduction in the number of'slits required will reduce the number ofchances for such tears to occur. Furthermore, I have found thatreducingthe amount of slitting required in the paper tubing in the formation ofthe bag makes the bag easier to run on the bag machine. Accordinglyanother object of the present invention is to provide an improvedmulti-ply leakproof bag in which less slitting of the plies will berequired than heretofore.

In my opinion it is not feasible to manufacture bags of the type usedfor carbon black without some slitting of the paper tubing for formingthe bottom section. In multi-ply bags the slits of the inner plies areof primary importance, and in the bags now commonly used for carbonblack I have found that leaks are more likely to start at the ends ofthe slits of the inner plies. Therefore an additional object of thepresent invention is to provide a bag bottom construction for amulti-ply bag in which there will not only be fewer such slits but inwhich the slit portions of the inner ply will ultimately be sopositioned as to be subjected to a minimum amount of strain from thepressure set up in the packed bag incidental to its handling. 7

The manner in which these objects and other "advantages are obtained inmy improved bag bottom construction, will be pointed out in the courseof the following brief description with reference to the accompanyingdrawings.

In the drawings:

Fig. 1 is a view, in perspective, of the multi-ply paper tubing fromwhich my bag is made, showing the first folding of the tubing to makethe bellows-like side portions of the bag, and also showing the slittingof the tubing as required for my improved bag bottom construction;

Fig. 2 illustrates the bottom forming portion of the-multi-ply-papertubing with the first stage of the bottom folding having taken place andwith the paste then having been applied to the bottom;

Fig. 3 is a similar view illustrating the same bottom portion, showingthe inner main flap of the bottom folded over onto the bottom in thenext stage of the forming of the bag bottom; Fi '4 is -a view of thecompleted bag '"b-otto'm 3 with the outer main flap of the bottom foldedover on the inner main flap, a portion of the outer ply of the paperbeing shown torn away to show the underlying ply and paste line moreclearly;

Fig. 5 is a perspective view, drawn to a smaller scale, of the completedbag showing the bag opened out and ready for filling.

For the sake of simplicity in illustrating my improved bag bottomconstruction, the drawings show the bag as formed of only two plies,thus an inner ply and an outer ply. Generally for carbon black bags, atleast three plies are used, in which case two plies take the place ofthe single outer ply which I have shown in the drawings. It is to beunderstood therefore that a double ply or double thickness of the paperwould probably be used for the single outer ply shown in the drawingsand that two or more thicknesses or plies could be substituted also forthe single inner ply as well as for the single outer ply of thedrawings.

While my invention requires a minimum .of two plies or two thicknessesof paper, my invention can be carried out with any reasonable number ofthicknesses or plies. The plies will constitute two groups in any event,thus an outer ply or group of plies and an inner ply or group of plies,corresponding to the outer and inner plies of the drawings. Thedifferent plies or thicknesses of paper are secured together :by spotpasting, and, in order to form the bag tube each ply has a separatelongitudinal seam, the longitudinal seams being staggered, all of thisbeing customary and well known in multi-ply bag construction.

Throughout the accompanying drawings the reference character Itindicates the outer ply, which may be regarded as representative of theouter group of plies as previously mentioned, and l I similarlyindicates the inner ply.

Referring first to Fig. l, the bag tubing [2, composed of two plies Illand H is given the longitudinal folds l3, M, [5 on each side in theusual manner to form the bellows-like sides for a square-bottom bag. Apair of slits is out in each of the plies, thus the slits I 6, I6 arecut in the outer ply l0 and the corresponding slits l1, I! are cut inthe inner ply i I, the slits of each pair being equally spaced from thelongitudinal side folds and the slits H, ll on the inner ply H beingplaced closer together and being shorter than the slits l6, l6 of theouter ply 10. These slits are similar in arrangement to those now commonin multi-ply bags except that only one pair of such slits is made ineach ply instead of the customary two opposite pairs of slits in eachply.

After the longitudinal side folding and the slitting have taken place,as illustrated in Fig. 1, the end of the tubing from which the bottompart of the bag is to .be made is drawn out, folded and pressed, asshown in Fig. 2, so as to form two similar trapezoidal main bottomsections i8 and i9 in the customary manner. The pair of slits l6 (Fig.l) in the outer ply IE will cause an outer lateral flap 28 (Fig, 2) toextend from one end of the two main bottom sections [8 and I9, thelength of the side edges 2| of the flap 20 corresponding to the lengthof the slits l6. Similarly the pair of slits 1? (Fig. 1) in the innerply il will result in a smaller inner lateral ilap 22 (Fig. 2) with sideedges 23 determined by the length of the shorter slits ll. The innerflap 22 is centrally spaced within the outer flap 20. The formation andarrangement of such lateral flaps is old in the art. However, contraryto the established practice, these outer and inner lateral flaps 20 and22 are formed at one end only of the main bottom sections [8 and I9since the outer and inner plies each have only one pair of slits insteadof the customary two pairs, as previously mentioned.

When the main bottom sections [8 and 3, with the outer andinner endlateral flaps 20 and 22, have been arranged as shown in Fig. 2, thepaste is applied in the usual manner in two broad parallel paste strips24 and 25 joined by a transverse paste strip 26 at one end over theflaps 26 and 22, and thus having the paste cover the areas indicated bythe stippling in Fig. 2. The paste strips 24 and 25 are preferably madeas wide as possible while still leaving a slight margin between theinside edges of these paste strips 24 and 25 and theadjacent edges ofthe paper, and also leaving a slight margin between the outer edges ofthese paste strips and the outer edges of the outer lateral flap 20.This is necessary so that the paste will not be pressed beyond theseedges of the paper in the finished bag.

After the applicagon of the paste along the paste strips 24, 25, 26, thebottom forming portion of the bag is folded over on itself on the creaseline 27 and thus the bottom portions will be arranged in the formationshown in Fig. 8, this folded over portion forming the inner maintriangular fold 28, which is pressed against the underlying bottomsections. Since the paste strips 24 and 25 extend over both theoverlying and underlying faces beneath this main triangular fold 28,there is practically no possibility of any failure in the two pasteseams which secure this main fold 28 to the underlying bag bottomsections. Furthermore, since the plies in the main triangular fold 28have not been slit, if any shifting of the bag contents is to take placepast or through this main fold 28, such sifting must occur either at theinner fold corners 29 at the tip of the main fold 28 or between thesecorners 29 and the adjacent inner edges of the paste strips 24 or 25.

After the inner triangular main fold 28 has been secured in place asillustrated in Fig. 3, the final step in the completion of the bagbottom consists in folding the opposite end of the bottom formingportion of the bag over on the crease line 30 and pressing this secondand outer folded-over portion 31 (Figs. 4 and 5) down on the underlyingbottom sections and down on top of the inner main triangular fold 28.

In my improved bag bottom the length and spacing of the pair of slits ofthe inner ply which determine the side edges of the inner and smallerlateralflap 22 are so arranged that when the outer portion 3| isfinally. folded over on top of the inner main triangular fold 28, thecorners 32 of the flap 22 of the inner ply N (Fig. 4), formed at theinner ends of the slits of the inner ply, will overlie the inner maintriangular fold 28 but will be located close to its edges. Lo eating theslit corners 32 at these points has two distinct advantages. The slitcorners of the inner ply represent the points at which the tearing ofthe bag paper is most likely to occur when strain is produced in thepacked bag. By having the strong unslitted inner main triangular fold ofthe bottom extending under these corners and capable of withstanding anyreasonable strain occasioned by pressure from the filled bag, thesecorners 32 are guarded and protected, and the possibility of any tearingof the inner ply of paper occurring at these corners after the bag iscompleted is reduced to a minimum.

If any sifting is to occur from the folded-over portion 3| of the bagbottom this would be most likely to take place at the slit corners 32.Material sifting from these corners 32 would be obliged to pass throughthe pasted seams in some direction in order to escape from the bagbottom. The most likely avenue of escape would be along an outer edge 33of the inner main triangular fold 28, thus, for example, in thedirection indicated by the arrow as in Fig. 4. The reason for this, asapparent, is that when the outer flap 20 is pasted down over thisportion of the bottom, the difference in level of the two underlyingsurfaces along the ridge or fold line 33 increases the difiiculty ofproducing a perfect seal along such line, this difference in level ofthe two underlying surfaces along such fold line amounting to at leastfour thicknesses of paper. The side portions of the flap 20 whichconstitute the sealing strips over this part of the bottom area, whetherconstituting one or two thicknesses of paper, will always be at leastthree thicknesses of paper less than the thickness of the triangularfold section 28, and the reduced thickness of these sealing stripsincreases the possibility of better sealing. Furthermore, since thepaste has been applied both to the underside of the flap 20 and also tothe underlying paper surface, which double application of paste extendsup to the ridge or fold 33, and since the side portions of the flap 20extend for a substantial distance beyond the corners 32 and the obliquedistance through the paste seam in the direction of the arrow :c is evengreater, I have found that when my bag bottom is made exactly as shownin Fig. 4, the likelihood of any material sifting out along the foldedouter edges of the portions 28 or 3! of the bag bottom is almostnegligible. This fact is another noticeable distinguishing featurebetween; my improved bag bottom and the bottoms of bags now commonlybeing used for carbon black and the like.

Previously when considering the possibility of leakage occurring fromthe inner main fold 28, I have explained that such leakage would have tostart at or near the inner corners '29. From such points the only likelyavenues of escape of the material would also be along the same ridge orfold lines 33. Assuming that the material might sift part of thisdistance along such an avenue, it would still have to travel a path suchas indicated by the arrow 3: in Fig. 4. The avenue of escape along thispath, as already explained, has been most effectively sealed as theresult of the improvements in my bag bottom.

Thus I provide my bag bottom with an inner triangular unslitted mainfold 29, extending a substantial distance over the bag bottom, and acorresponding outer folded-over portion 3|, overlapping the inner mainfold 28. The two plies, or groups of plies, from which the bag tube isformed, are slitted in the outer folded-over por-- tion 3| so as to formtwo lateral flaps constituting the outer flap 29 and the inner flap 22,the inner flap being located entirely within the outer flap. The twopairs of slits which form the two lateral flaps 20 and 22 are soarranged and proportioned that the inner ends of the slits forming theinner flap will be positioned on the inner main fold 28 near the bordersof the same when the inner flap is finally secured in place on the bagbottom, and the side edges 2| of the outer flap 20 will extend to andover the borders of the inner main fold 23 at points a substantialdistance out from the side edges of the inner flap 22. Consequently theouter flap 20 not only provides a protective outer sealing layerextending over and beyond the side edges of the inner flap 22, but theside portions of the outer flap also enable two supplementaltriangularly-shaped sealed areas to be provided beyond the borders ofthe inner main fold 28 and the outer foldedover portion 3|, effectivelyblocking the most likely channels through which sifting of the bacontents from the bag bottom could otherwise possibly occur. In theseadded sealed areas, as well as along the paste seams sealing the innerand outer folds 28 and 3| to the body of the bag, double application ofpaste, thus application of paste to both opposed faces of the paperwhich are sealed to each other, has been provided and in this manner anypossible failures in the paste seams are practically eliminated.

Finally my improved bag bottom, whether the bag tubing is formed withtwo plies or with more than two plies, is so made as to withstand heavystrains; the amount of slitting of the plies in the forming of the bagbottom has been reduced by one-half, making the bag easier to run on thebag machine; and possibility of any tearing occurring at the slits ofthe inner ply has been considerably lessened.

I claim:

A sift-proof bag bottom of the character described formed on the bottomend of a multiply bag tube, said bag tube initially having a pair oflongitudinal slits centrally spaced in the bottom end of one side wallof the outer ply and a pair of centrally spaced longitudinal slits inthe bottom end of the same side wall of the inner ply, said slits insaid inner ply being considerably shorter and considerably nearertogether than the slits in said outer ply, said bottom end of said tubepressed into two identical main portions together comprising asubstantially diamond-shaped bottom section having one end substantiallytriangularly-shaped, said pairs of slits forming tabs on said outer andsaid inner plies extending from the other end of said bot tom section,said triangularly-shaped end folded over and secured to the bag bottomand extending more than half way across the bag bottom, said other endfolded over on said triangularlyshaped end and secured thereto and tosaid bag bottom, the tab of said inner ply being entirely superimposedon said triangularly-shaped end, and the tab of said outer ply extendingconsiderable distance beyond the edges of said triangularly-shaped endwhere said ends are overlapped.

MERLE E. CRAIG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number

